1. Field of the Invention
The present invention relates to an air-spring vibration isolation device for supporting an object to be isolated from vibration such as a precision instrument while isolating the object from vibration transmitted from the floor to the vibration isolation device.
2. Description of the Related Art
In a typical air-spring vibration isolation device, vibration transmitted from the floor to a stationary housing of the vibration isolation device is prevented from being transmitted to a vibration-free movable base of the vibration isolation device by supporting the vibration-free movable base on the stationary housing via an airtight pressure chamber (airtight flexible member) while introducing regulated air pressure into the airtight pressure chamber.
To obtain further improvement in vibration isolating performance, this type of air-spring vibration isolation device using air pressure, which is provided with a movable top plate that moves up and down by the airtight pressure chamber without the vibration-free movable base being directly supported by the airtight pressure chamber, wherein the vibration-free movable base is allowed to swing (oscillate) relative to the movable top plate by a structure in which the movable top plate and a mounting plate portion of the vibration-free movable base are arranged to face each other so as to be in point contact with each other via a dome-shaped (hemispherical) contacting portion installed between opposed surfaces of the movable top plate and the mounting plate portion at a planar center thereof, is known in the art.
In this particular type of air-spring vibration isolation device that uses such a dome-shaped contacting portion, the movable top plate descends toward the stationary housing to release the point-contacting engagement of the movable top plate with the mounting plate portion via the dome-shaped contacting portion if the air pressure applied to the airtight pressure chamber is removed, e.g., during the time when the vibration isolation device is in a non-operational state. Thereafter, when the vibration isolation device resumes operating, air pressure is again introduced into the airtight pressure chamber to move up the movable top plate via the dome-shaped contacting portion. Although it is a matter of course that the two-dimensional positioning of the vibration-free movable base relative to the stationary housing is precisely established in advance, this precise two-dimensional positioning of the vibration-free movable base relative to the stationary housing is lost once the point-contact engagement of the movable top plate with the mounting plate portion of the vibration-free movable base is released, which proves it to be impossible to reproduce the original vibration isolating performance.